1. Field of the Invention
The present invention relates to a display device having a combined display-panel unit that is comprised of a main display panel and a transparent display panel overlapping the main display panel.
2. Description of the Related Art
JP-A-10-91087, which corresponds to U.S. patent application Ser. No. 09/899,566, and EP 0775 291 B1, which corresponds to JP-A-10-504101, disclose a vehicle combination meter having a front display panel that is comprised of a transparent electro-luminescent (EL) panel and a back display panel. When the back display panel displays an information pattern, the back display panel is illuminated while the front display panel is turned off to make the information patter visible. On the other hand, when the front display panel displays an information pattern, the illumination of the back panel is turned off. That is, the display is changed from one to another by turning on or off the illumination of the panels.
In the above combination meter, either one of the front and back panels can display the information pattern. If the information patterns are displayed by both panels concurrently, it is difficult for a viewer to recognize the information patterns correctly.
Therefore, a main object of the invention is to provide a display device having an improved combined-display-panel unit.
Another object of the invention is to provide a combined-display-panel unit that includes a main panel and a transparent panel, both of which can display clear information patterns concurrently.
According to a main aspect of the invention, a display device includes a main display panel, a transparent display panel disposed to cover the first display panel, and a control unit controlling relative visibility of the main and transparent displays to have a user selectively recognize information patterns displayed by both the display panels. Therefore, it is possible to indicate various information patterns by using any one of the panels or both panels, as the occasion demands.
According to another aspect of the invention, the control unit of the above display device controls luminance of at least one of the main and transparent display panels. Therefore, a user can easily recognize the level of importance or seriousness of the information. For this purpose, it is possible to increase the luminance of one of the display panel that indicates more important information patterns. It is also possible to increase the luminance for a predetermined period, and to change color or size of the transparent display.